Recently, a photoelectric transducer for directly converting solar energy into electric energy, the so-called solar cell, has been highly expected as a future-generation energy source in the point of view of problems on earth environment. The photoelectric transducer to be utilized as the solar cell has various types such as those using a composite semiconductor or an organic material, but the mainstream today is of the type using a silicon crystal. An amorphous silicon or a poly-crystal silicon may be widely utilized.
FIG. 5 shows schematically a sectional view of an example of a conventional solar cell. In the conventional solar cell, a n+ layer 11 is formed on a light-receiving surface of a p-type silicon substrate 10 as a semiconductor substrate so as to make a pn junction formed by the p-type silicon substrate 10 and the n+ layer 11. On a first principal surface constituting the light-receiving surface of the p-type silicon substrate 10, there are generated an antireflection film 12 and a silver electrode 13, respectively. Besides, the silver electrode 13 includes a bus bar electrode to be connected to an inter-connector, and a finger electrode extending from the bas bar electrode.
Further, a p+ layer 15 is generated on a second principal surface opposed to the light-receiving surface of the p-type silicon substrate 10. An aluminum electrode 14, and a silver electrode 16 which is connected to the inter-connector, are generated on the back surface of the p-type silicon substrate 10, respectively.
However, in the conventional structure as above, there are problems that an incident light beam may be disturbed by the silver electrode 13, the bus bar electrode, and the finger electrode on the first principal surface to thereby cause a loss by a shadow, and, in addition, carrier re-combination loss may occur under the silver electrode 13. Therefore, it may be necessary that a surface-area factor of the silver electrode 13, the bus bar electrode, and the finger electrode on the first principal surface be small as much as possible.
Then, in order to reduce the surface-area factor of the silver electrode 13 on the first principal surface, and, in addition, to prevent the carrier re-combination loss under the silver electrode 13, a Metal Wrap Through (MWT)-type solar cell as shown schematically in a sectional view of FIG. 6 has been proposed.
In the MWT-type solar cell, a through electrode 19 passing through a through-hole preliminarily penetrated in the silicon substrate 10 causes a part of a silver electrode 17 on a first principal surface to be wired to a silver electrode 18 of a second principal surface. According to such a structure, a surface-area factor of the silver electrode 17 on the first principal surface can be reduced.
In such a solar cell, it is necessary that the silver electrode 18 coupled on the second principal surface which is wired by the silver electrode 17 on the first principal surface and the through electrode 19, be electrically isolated from an aluminum electrode 14 on the second principal surface. Therefore, as proposed in the document 1 below, an n+ layer 11 between the silver electrode 18 on the second principal surface of the p-type silicon substrate 10 and the aluminum electrode 14 is removed by laser ablation to generate a junction separation portion 20.    Non-Patent Document 1: Filip Granek, A systematic approach to reduce process-induced shunts in back-contacted mc-Si solar cells, 4th-WCPEC(2006), Hawaii
In the MWT-type solar cell as shown in FIG. 6, the wider the surface area of the silver electrode 18 becomes, the better it is at the point of view of the mutual adhesion strength and a contact resistance thereof, because the silver electrode 18 must be connected to the inter-connector. Nonetheless, to widen the silver electrode 18, it is necessary to eliminate the aluminum electrode 14 at the portion of the silver electrode 18, and, in addition, generate the junction separation portion 20 around the silver electrode 18. Therefore, as the surface area of the silver electrode 18 is widened, the surrounding length of the junction separation portion 20 becomes longer so as to cause the problems that an insulating resistance may be reduced.
The reduction of the insulating resistance may cause the reduction of a fill factor (FF) in the solar cell characteristics. Further, as the surface area of the silver electrode 18 is widened, the surface area of the aluminum electrode 14 is reduced so that there are the problems that the surface area of the p+ layer 15 under the aluminum-silicon alloy is also reduced and Ise and Voc of the solar cell characteristics are reduced.
In view of the above-mentioned circumstances, it is a feature of the example embodiment presented herein to provide an improved photoelectric transducer as a solar cell with highly efficiency for improving an insulating resistance by shortening a surrounding length of a junction separation portion 20.
In order to solve the above problems, in a photoelectric transducer of the type where a light-receiving surface electrode is wired to another electrode on a back surface via a through electrode passing through a semiconductor substrate of a first conductive type, the photoelectric transducer of the present invention comprises a junction separation portion made around the through electrode on a back surface of the semiconductor substrate; a dielectric layer formed for covering the junction separation portion, the through electrode penetrating the dielectric layer; and a back electrode provided on the dielectric layer and coupled to the through electrode which is connected to the light-receiving surface electrode.
In the other words, a photoelectric transducer of the present embodiment comprises a semiconductor substrate of a first conductive type; a substrate through-hole penetrated through the semiconductor substrate; a semiconductor layer formed on a part of a light-receiving surface and a back surface of the semiconductor substrate, the semiconductor layer being of a second conductive type; a substrate conductive layer formed on the back surface of the semiconductor substrate, the substrate conductive layer having an opening portion for surrounding the substrate through-hole; a junction separation portion for electrically isolating the substrate conductive layer from the semiconductor layer, the junction separation portion being made around the substrate through-hole; a dielectric film formed on the back surface of the semiconductor substrate for covering the junction separation portion, the dielectric film having a dielectric-film through-hole successive to the substrate through-hole; a back electrode provided on the dielectric film, the back electrode being electrically connected to a though electrode passing through the substrate through-hole and the dielectric-film through-hole; and a light-receiving surface electrode provided on the light-receiving surface of the semiconductor layer, the light-receiving surface electrode being electrically coupled to the semiconductor layer and connected to the back electrode via the though electrode.
According to this construction, the surrounding length of the junction separation portion can be shortened to improve an insulating resistance. Further, the surface area of an aluminum electrode can be enlarged to improve a fill factor (FF), Ise, and Vco of the solar cell characteristics. Thereby, a solar cell with highly efficiency can be provided according to the present invention.
According to a specific embodiment of a photoelectric transducer, it is preferable that the back electrode have an outer diameter larger than the diameter of the junction separation portion. Hereby, the surrounding length of the junction separation portion can be shortened to improve an insulating resistance. At the same time, the outer diameter of the back electrode can be enlarged to enhance the mutual adhesion strength and minimize a contact resistance thereof in the case where it is connected to an inter-connector.
According to another specific embodiment of a photoelectric transducer, it is preferable that the dielectric film lies also on a part of the substrate conductive layer and that the outer diameter of the back electrode is larger than the diameter of the opening portion on the substrate conductive layer. Hereby, the outer diameter of the back electrode can be enlarged to enhance the mutual adhesion strength and minimize a contact resistance thereof in the case where it is connected to an inter-connector.
It is a feature of the present embodiment to provide a manufacture method for manufacturing a photoelectric transducer comprising the steps of: forming a substrate through-hole penetrating through a semiconductor substrate of a first conductive type; generating a semiconductor layer on the semiconductor substrate; forming a substrate conductive layer on the back surface of the semiconductor substrate except for the portion of the substrate through-hole; making a junction separation portion around the substrate through-hole on the back surface of the semiconductor substrate; forming a dielectric film on the back surface of the semiconductor substrate and the substrate conductive layer for covering the junction separation portion, the dielectric film having a dielectric-film through-hole successive to the substrate through-hole; providing a though electrode inside the substrate through-hole and the dielectric-film through-hole, and providing a back electrode on the dielectric film; and providing a light-receiving surface electrode on the light-receiving surface of the semiconductor layer, the light-receiving surface electrode being electrically coupled to the semiconductor layer and connected to the back electrode via the though electrode.
Hereby, a photoelectric transducer of the present embodiment can be manufactured.
According to the present embodiment, in the photoelectric transducer of the type where the light-receiving surface electrode is wired to the back surface via the substrate through-hole penetrated through in the silicon substrate, the back electrode is provided via the dielectric film above the junction separation portion made around the substrate through-hole in the back surface of the semiconductor substrate to shorten the surrounding length of the junction separation portion and to improve an insulating resistance.
Further, the surface area of the aluminum electrode constituting the substrate conductive layer can be enlarged to improve the performance of a solar cell. Thus, a solar cell with highly efficiency can be provided.